Madhyamik Class 10 Life Science Solved Paper 2023

Madhyamik Class 10 Life Science Solved Paper 2023

LIFE SCIENCE

Time: 3 Hours 15 Minutes

(First 15 Minutes for reading the question paper only, 3 Hours for writing) 

Full Marks: For Regular Candidates – 90

For External Candidates – 100

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Regular candidates will answer questions from Groups A, B, C and D. External candidates will answer questions from Group E.

(Special Instructions for visually handicapped candidates)

Answer Question 4.1(A) instead of Question 4.1 in Group D. Instruction on how many questions from a group must be attempted is provided at the beginning of the group.

Group ‘A’
(All questions are compulsory)

1. Choose the correct answer for each question and write it with its respective-serial number: [1 × 15=15]

Question 1.1

Which of the following is not a structural feature of an Axon?

1. Node of Ranvier
2. Myelin sheath
3. Nissl granule
4. Schwann cell

Answer

Nissl granule

Question 1.2

Which of the following is a function of the hormone ADH?

1. Increases blood pressure by constricting arterioles
2. Helps in the production of sperm and ovum in adult life
3. Converts glucose into glycogen and stores in hepatic and muscle cells
4. Causes the development of the nervous system and maintains its normal function

Answer

Increases blood pressure by constricting arterioles.

Question 1.3

Cornea, Choroid, Lens, Aqueous humour, Iris, Vitreous humour – how many of these are refractory media of the eyeball?

1. 3
2. 4
3. 5
4. 6

Answer

4

Question 1.4

Which of the following is correct regarding the Chemical Composition of nucleotide?

1. 5 – C Sugar + Phosphoric Acid = Nucleotide
2. Nitrogenous base + Phosphoric Acid = Nucleotide
3. 5 – C Sugar + Nitrogenous base = Nucleotide
4. 5 – C Sugar + Nitrogenous base + Phosphoric Acid = Nucleotide

Answer

5 – C Sugar + Nitrogenous base + Phosphoric Acid = Nucleotide.

Question 1.5

Which of the following pair is correct in respect of the process of cross-pollination?

Mode of pollination	Name of the plant
(a) Anemophilous	Mango
(b) Hydrophilous	Paddy
(c) Entomophilous	Hydrilla
(d) Ornithophilous	Butea/Palash/Flame of the Forest

Answer

(d) Ornithophilous – Butea/Palash/Flame of the forest.

Question 1.6

Which of the following stages is not included under the Sporophytic generation in the alternation of generations of the fern?

1. Prothallus
2. Sorus
3. Sporangium
4. Spore mother cell

Answer

Prothallus

Question 1.7

What is the ratio of the number of the genotypes BBRr and BBRR produced in the F₂ generation of dihybrid cross in Guineapig?

1. 2 : 1
2. 4 : 1
3. 1 : 2
4. 1 : 1

Answer

1 : 1

Question 1.8

Which two of the following genotypes represent the genotype of a pea plant with yellow coloured and wrinkled seed?

1. YYr, Yy
2. YYRr, YRR
3. yRR, yyRr
4. YYRR, yyrr

Answer

YYrr or yyRr

Question 1.9

Which would be the genotypic and phenotypic ratio in the F₂ generation of a hybrid cross in case of incomplete dominance?

1. 2 : 1 : 1
2. 1 : 1 : 1
3. 1 : 2 : 1
4. 1 : 2 : 2

Answer

1 : 2 : 1

Question 1.10

Which of the following is not a tenet of Darwinism?

1. Inheritance of acquired character
2. Struggle for existence
3. Variation
4. Natural selection

Answer

Inheritance of acquired character

Question 1.11

Identify the features of homologous organs-

1. Different by structure but identical by origin and function
2. Different by origin and function but identical by structure
3. Different by origin but identical by structure and function
4. Identical by origin and structure but different by function

Answer

Identical by origin and structure but different by function

Question 1.12

Which reactants were used in the experiment of Miller and Urey regarding chemical origin of life?

1. Oxygen, Methane, Nitrogen dioxide
2. Water, Methane, Ammonia, Hydrogen
3. Methane, Hydrogen sulphide, Carbon monoxide
4. Nitrous oxide, Methane, Carbon dioxide

Answer

Water, methane, ammonia, and hydrogen

Question 1.13

Identify the correct sequence of the Nitrogen Cycle

1. Fixation of Nitrogen → Denitrification → Ammonification → Nitrification
2. Ammonification → Nitrification → Nitrogen Fixation → Denitrification
3. Nitrogen Fixation → Ammonification → Nitrification → Denitrification
4. Nitrification → Nitrogen Fixation → Denitrification → Ammonification

Answer

Nitrogen fixation → Ammonification → Nitrification → Denitrification.

Question 1.14

Decide which of the following pair of causes of depletion and victimised species is correct regarding the depletion of biodiversity-

1. Introduction of exotic species → One-horned Rhinoceros
2. Pollution → Royal Bengal Tiger
3. Global warming and climatic change → Polar Bear
4. Hunting and Poaching → Vulture

Answer

Hunting and Poaching → Vulture

Question 1.15

Which of the following phenomena occurs when chlorinated insecticides enter a food chain-

1. Biomagnification
2. Global warming
3. Eutrophication
4. Deafness

Answer

Biomagnification

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Group ‘B’

2. Answer 21 questions out of the 26 questions given below, as instructed. [1 × 21=21]

Question 2.1 – 2.6

Fill in the blanks (any five) [1 × 5=5]

1. Nastic movement is influenced and controlled by the ____ of an external stimulus.
2. ____ cell division maintains the number of chromosomes constant in a species.
3. The wrinkled shape of seed is a ____ trait.
4. Because of its ____ shape, the RBC of camel can withstand a considerable loss of water.
5. A disease related to air pollution is ____.
6. Nilgiri and ____ are both Biosphere Reserves.

Answer

1. Direction
2. Mitotic
3. Recessive
4. Biconcave
5. Bronchitis
6. Sundarbans

Question 2.2 – 2.6

Decide whether the following statements are True or False (any five): [1 × 5=5]

1. Auxin hormone inhibits the growth of apical bud and increases the growth of axillary bud.
2. Cell division becomes uncontrolled if the function of checkpoints becomes hampered.
3. Only one type of gamete is produced from a pea plant having genotype YyRR.
4. Both intraspecific and interspecific struggles might be observed among the different types of tigers in a forest.
5. Nitrous oxide is a greenhouse gas.
6. Triceps is a flexor muscle.

Answer

1. True. Auxin is a plant hormone that inhibits the growth of apical buds and stimulates the growth of axillary buds. This is known as apical dominance.
2. False. Checkpoints are essential for controlling cell division. If the function of checkpoints becomes hampered, cell division can become uncontrolled, leading to cancer.
3. False. A pea plant with genotype YyRR can produce two types of gametes: Yy and RR. This is because the Y and R genes are not linked, so they can segregate independently during meiosis.
4. True. Intraspecific competition occurs between individuals of the same species, while interspecific competition occurs between individuals of different species. Both types of competition can be observed among different types of tigers in a forest.
5. True. Nitrous oxide is a greenhouse gas that traps heat in the atmosphere. It is produced by a variety of sources, including agricultural activities, industrial processes, and the combustion of fossil fuels.
6. False. Triceps is an extensor muscle. It is responsible for extending the elbow joint.

Question 2.3

Match the words in column-A with the most appropriate words in column B and re-write the correct pair mentioning the serial no. of both columns (any five):-  [1 × 5=5]              

COLUMN – A	COLUMN – B
1. Meninges	(a) Decrease in the number of digits in the legs
2. Sexual reproduction	(b) Submergence of islands
3. Roller tongue	(c) Centromere
4. Evolution of the horse	(d) Telomere
5. Environmental problem of Sundarban	(e) Protects brain and spinal cord from mechanical injury
6. Attaches chromosome with spindle fibre	(f) Controlled by autosome
	(g) Occurs through the production of gametes and their union

Answer

Column A	Column B
1. Meninges	(e) Protects brain and spinal cord from mechanical injury
2. Sexual reproduction	(g) Occurs through the production of gametes and their union
3. Roller tongue	(f) Controlled by autosome
4. Evolution of the horse	(a) Decrease in the number of digits in the legs
5. Environmental problem of Sundarban	(b) Submergence of islands
6. Attaches chromosome with spindle fibre	(c) Centromere
7. Telomere	(d) Protects ends of chromosomes

Question 2.4

Answer in a single word or in a single sentence (any six) [1 × 6=6]

1. Choose the odd word and write it:
   Testosterone, Insulin, Progesterone, Oestrogen
2. What is the relation between the lens and the accommodation of the eye?
3. On the basis of the relationship in the first related pair of words, write a suitable word in the gap of the second pair.
   Mitosis: Equational division : : ____ : Reduction division
4. In spite of being pure in respect of one trait, what else could an organism be in respect of another trait?
5. Write one feature of the gene responsible for colour blindness.
6. Which theory can be reached from the comparative study of the embryos of different vertebrate animals?
7. Among the following four terms, one includes the other three. Find it out and write it: Shrinking of agricultural land, shortage of fresh water, problems of an ever-increasing population, deforestation
8. Write one feature of a biodiversity hotspot.

Answer

1. Insulin. The other three hormones are sex hormones.
2. The lens changes shape to accommodate for near and far objects.
3. Meiosis
4. Hybrid
5. It is carried by the X chromosome.
6. The theory of recapitulation
7. Deforestation. The other three are consequences of deforestation.
8. High level of endemism. A biodiversity hotspot is a region with a high number of endemic species.

Group ‘C’

3. Answer any 12 questions each in 2-3 sentences out of 17 questions given below:- [2 × 12=24]

Question 3.1

The two reflex actions, namely sneezing and coughing help in avoiding danger -justify the statement.

Answer

Sneezing and coughing are reflex actions that help to remove foreign particles from the respiratory tract. When a foreign particle enters the respiratory tract, it triggers a sensory neuron, which sends a signal to the brain. The brain then sends a signal to the respiratory muscles, which causes the person to sneeze or cough.

Question 3.2

How does the Gibberellin hormone cause the seeds to germinate and the plants to grow in height?

Answer

Gibberellins are plant hormones that promote growth. They do this by stimulating the production of enzymes that break down stored food reserves in the seeds. This allows the seeds to germinate and start growing. Gibberellins also promote cell elongation, which helps the plants to grow taller.

Question 3.3

Write one influence of each of the Thyroxine hormones on the heart and the RBC.

Answer

• Thyroxine is a hormone produced by the thyroid gland. It has a number of effects on the body, including increasing the heart rate, stimulating the metabolism, and increasing the production of red blood cells.
• RBC are red blood cells. They carry oxygen from the lungs to the tissues of the body. Thyroxine increases the production of RBC, which helps to improve the oxygen supply to the tissues.

Question 3.4

Explain the following two terms:-

1. Ganglia
2. Synapse

Answer

1. Ganglia are clusters of nerve cells that are located outside the central nervous system. They are responsible for relaying sensory information to the central nervous system and for controlling motor functions.
2. Synapse is the junction between two neurons. It is the point where the electrical signal from one neuron is transmitted to the next neuron.

Question 3.5

Write two features of Amitotic cell division.

Answer

Features of amitotic cell division:

• It is a type of cell division that does not involve the formation of a spindle.
• The chromosomes do not condense during amitotic cell division.

Question 3.6

Mention any two phenomena during G₁ phase of Interphase.

Answer

G1 phase is the first phase of the interphase. It is the phase in which the cell grows and prepares for DNA replication.

Phenomena during G1 phase:

• The cell grows in size.
• The cell synthesizes proteins and RNA.
• The cell replicates its DNA.

Question 3.7

Explain the process of segmentation with the help of a proper example of plants.

Answer

Segmentation is the process by which the zygote divides into a number of cells, called blastomeres. The blastomeres then divide further to form the embryo. Segmentation is a type of cell division that is found in many animals, including humans.

Question 3.8

What is the importance of genetic counselling in arranging a marriage?

Answer

Genetic counselling is the process of providing information and advice to people about their genetic risks. It can be used to help people make informed decisions about their health and reproduction. Genetic counselling is important in arranging a marriage because it can help to identify couples who are at risk of having children with genetic disorders.

Question 3.9

Write two reasons behind the selection of pea plants by Mendel for his experiments on heredity.

Answer

Reasons for the selection of pea plants by Mendel for his experiments on heredity:

1. Pea plants are easy to grow and cross-pollinate.
2. They have a relatively short life cycle.

Question 3.10

Judge with the reason the probability of what percentage of the children born to a colour-blind father and a completely normal mother would be colour-blind.

Answer

The probability of a child being colour-blind if the father is colour-blind and the mother is normal is 50%. This is because the father will pass on his colour-blind gene to all of his children, regardless of the mother’s genotype. The mother, on the other hand, will only pass on her normal gene to half of her children.

Question 3.11

An inherent trait of organisms is the prodigality of reproduction; as a result, the number of organisms increases in a geometric proportion – justify the validity of the statement with two proper examples.

Answer

The prodigality of reproduction is an inherent trait of organisms. This means that organisms tend to reproduce in large numbers. This is because the chances of survival of an individual organism are low. By reproducing in large numbers, the organisms increase their chances of survival.

Question 3.12

How do worker bees communicate the information to the other worker bees of the hive when they spot any source of food?

Answer

Worker bees communicate the information about a food source to other worker bees by using a waggle dance. The waggle dance is a series of movements that the worker bee performs in front of the other worker bees. The movements of the waggle dance indicate the distance, direction, and quality of the food source.

Question 3.13

What do you mean by natural selection?

Answer

Natural selection is the process by which organisms that are better adapted to their environment are more likely to survive and reproduce. This means that the organisms with the traits that are most helpful in their environment are more likely to pass on those traits to their offspring. Over time, this can lead to the evolution of new species.

Question 3.14

One of the problems associated with the ever-increasing population is the destruction of wetlands. Mention any two consequences of this.

Answer

Wetlands are important ecosystems that provide a variety of benefits, including flood control, water purification, and habitat for wildlife. However, wetlands are also vulnerable to destruction, and this is a problem that is becoming more severe as the human population grows.

Two consequences of the destruction of wetlands are:

1. Increased flooding. Wetlands help to absorb excess water during floods, so their destruction can lead to more flooding in surrounding areas.
2. Decreased water quality. Wetlands help to filter pollutants out of water, so their destruction can lead to decreased water quality.

Question 3.15

The invasion of exotic species causes a reduction in biodiversity to establish the validity of this statement with two examples with reference to India.

Answer

In India, two examples of exotic species that have caused a reduction in biodiversity are Nilgai and Water hyacinth. Nilgai are large antelope that are native to Africa, but they were introduced to India in the 19th century. Nilgai has since spread throughout much of India, and they have been a major factor in the decline of native grazing animals such as the blackbuck.

Question 3.16

Write the names of one endangered plant and one endangered animal species of the Eastern Himalayas biodiversity hotspot.

Answer

Here are some other endangered plant and animal species of the Eastern Himalayas biodiversity hotspot:

1. Snow leopard
2. Himalayan tahr

Question 3.17

Write one role of Joint Forest Management (JFM) and People’s Biodiversity Register (PBR) each for the conservation of biodiversity.

Answer

• Joint Forest Management (JFM): JFM involves local communities in the management of forests, which helps to ensure that forests are managed in a sustainable way and that local communities benefit from them.
• People’s Biodiversity Register (PBR): PBRs document the traditional knowledge of local communities about biodiversity, which helps to protect this knowledge from being lost and can be used to conserve biodiversity in a number of ways.

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Group ‘D’
(Long answer type questions)

4. Write all 6 questions or their alternatives given below. Sightless candidates have to answer question no. 4.1(A) instead of question no. 4.1. The marks allotted for each question is 5 (the division of marks is either 3+2, 2+3 or 5) [5×6=30]

Question 4.1

Draw a scientific diagram of the vertical section of a human eyeball and label the following parts:    [3+2=5]

1. Choroid
2. Lens
3. Cornea
4. Vitreous humour

Answer

OR

Draw a scientific diagram of the anaphase stage of mitotic cell division in an animal cell and label the following parts-  [3+2=5]

1. Centromere
2. Daughter chromosome
3. Polar region
4. Spindle fibre

Answer

(For Sightless Candidates Only)

Question 4.1 (A)

Write one function of each of the following five parts of the human eyeball:  [1×5=5]

1. Cornea
2. Lens
3. Choroid
4. Vitreous humour
5. Retina

Answer

a. Cornea

1. The cornea is the clear front part of the eye that helps to focus light.
2. It is made up of a layer of cells that are arranged in a way that allows light to pass through them without being scattered.

b. Lens

1. The lens is a transparent structure that helps to focus light onto the retina.
2. It is located behind the cornea and is held in place by the ciliary muscles.

c. Choroid

1. The choroid is a layer of tissue that lies between the retina and the sclera.
2. It contains blood vessels that supply the retina with blood.

d. Vitreous humour

1. The vitreous humour is a clear gel that fills the space between the lens and the retina.
2. It helps to keep the shape of the eyeball and to transmit light to the retina.

e. Retina

1. The retina is a layer of tissue at the back of the eye that contains light-sensitive cells.
2. These cells convert light into electrical signals that are sent to the brain.

OR

Mention three changes occurring during the Anaphase stage of mitosis in an animal cell. Write the names of any two structural parts of the eukaryotic chromosome.  [ 3+2=5]

Answer

Here are three changes occurring during the Anaphase stage of mitosis in an animal cell in very short points:

1. Centromeres split, and sister chromatids separate.
2. Mitotic spindle elongates, pulling sister chromatids to opposite poles.
3. Nuclear envelope breaks down, allowing chromosomes to enter the cytoplasm.

Here are the names of two structural parts of the eukaryotic chromosome in very short points:

1. Centromere: A specialized region of the chromosome that is involved in cell division.
2. Chromatids: The two identical copies of a chromosome that are produced during DNA replication.

Question 4.2

Explain the following three significances of cell division-

• Growth
• Repair
• Reproduction

Tabulate the site of occurrences of meiotic cell division in the living world.  [3+2=5]

Answer

The three significances of cell division in very short points:

• Growth: Cell division is essential for the growth of multicellular organisms. As cells divide, they increase in number and size, which allows the organism to grow.
• Repair: Cell division is also important for the repair of damaged cells. When cells are damaged, they can divide to produce new cells that replace the damaged ones.
• Reproduction: Cell division is necessary for sexual reproduction. During sexual reproduction, two cells divide to produce four cells, each of which contains half the genetic information of the parent cells. These four cells can then fuse together to form a new organism.

Here is a table of the site of occurrences of meiotic cell division in the living world:

OR 

Explain the process of micropropagation. Distinguish between asexual and sexual reproduction on the basis of the following three features –

• No. of Parental organisms
• Cell Division
• Origin of variation [2+3=5]

Answer

The process of micropropagation in very short points:

• Micropropagation is a technique for rapidly producing clones of plants from a single plant.
• It is done by taking a small piece of tissue from a plant and growing it in a sterile culture medium.
• The tissue will then divide and produce new plants, which are genetically identical to the parent plant.

Here is a table that distinguishes between asexual and sexual reproduction on the basis of the three features you mentioned:

Question 4.3

With the help of a checkerboard show the phenotypic ratio of offspring produced in F₂ generation as a result of a cross between a pure black coloured and rough-haired guinea pig and a pure white and smooth-haired guinea pig. “Father plays the main role in the determination of sex of the offspring” – justify the statement with the help of a checkerboard. [3+2=5]

Answer

Pure Black and Rough: BBRR

Pure White and smooth: bbrr

F1 generation: BbRr (Hybrid Black and Rough)

Phenotypic ratio = 9 : 3 : 3 : 1

The father contributes an X chromosome to all of his offspring, while the mother contributes either an X or a Y chromosome. This means that the father’s X chromosome will always be present in his offspring, while the mother’s X chromosome may or may not be present.

Therefore, the father has a greater influence on the sex of the offspring than the mother.

OR

Write three reasons behind Mendel’s success. Establish a relationship between phenotype and genotype with the help of proper examples. [3+2=5]

Answer

The three reasons behind Mendel’s success:

1. He used purebred pea plants. This allowed him to control the genetic makeup of the plants and to isolate the effects of individual genes.
2. He conducted large-scale experiments. This allowed him to collect enough data to draw statistically significant conclusions.
3. He used statistical analysis. This allowed him to analyze his data objectively and to identify patterns that would have been invisible to the naked eye.

Here is the relationship between phenotype and genotype with the help of proper examples:

• Phenotype is the physical appearance of an organism, while genotype is the genetic makeup of an organism.
• The phenotype of an organism is determined by its genotype. For example, a pea plant with the genotype “AA” will have the phenotype “purple flower.”

Question 4.4

Explain the theory of Darwin with regard to the lengthening of the neck of a giraffe. What do you mean by ‘Hot Dilute Soup’? [3+2=5]

Answer

The theory of Darwin with regard to the lengthening of the neck of a giraffe:

• Giraffes with longer necks had an advantage over giraffes with shorter necks. They could reach higher leaves, which meant they had more food to eat.
• Over time, the giraffes with longer necks were more likely to survive and reproduce. This meant that the genes for long necks were more likely to be passed on to the next generation.
• As a result, the giraffe population gradually evolved to have longer necks.

The term “Hot Dilute Soup” is a metaphor for the soup of genetic variation that exists in all populations. This soup is constantly being stirred by mutation, recombination, and gene flow. As a result, there is always a variety of different genotypes present in a population, even if the phenotype may appear to be relatively uniform.

OR

Construct the sequence of major events of organic evolution with the help of a schematic diagram. Give two examples of the problem-solving ability of chimpanzees. [3+2=5]

Answer

Major events of organic evolution

Problem Solving in Chimpanzees:

• This animal is quite clever and can prepare a tool with a small branch of a tree. After defoliating the tip of the twig, it is crushed to prepare it like a brush. Then the brush is inserted into the termite mound. This stick like brush is then pulled out when quite a good number of termites may be collected for eating.
• The chimpanzee can also break and open nuts with stones which resemble the “hammer and anvil” technique to get the edible seed.

Question 4.5

Write one symptom of each of two diseases which might be caused if suspended particulate matter enters into the respiratory tract through inspiration. Construct the sequence of events when agricultural runoff is drained into water bodies. [2+3=5]

Answer

The two diseases that might be caused by suspended particulate matter (SPM) entering the respiratory tract through inspiration, along with one symptom of each:

• Asthma: A chronic lung condition that causes inflammation and narrowing of the airways. Symptoms include shortness of breath, wheezing, and coughing.
• Chronic obstructive pulmonary disease (COPD): A group of lung diseases that includes emphysema and chronic bronchitis. Symptoms include shortness of breath, coughing, and wheezing.

Here is the sequence of events when agricultural runoff is drained into water bodies:

1. Rainwater or snowmelt flows over the land surface, picking up sediment, nutrients, and pollutants from agricultural fields.
2. The runoff enters streams and rivers, where it can further pick up pollutants from the surrounding environment.
3. The runoff eventually reaches lakes, where it can contribute to eutrophication.
4. The runoff can also reach the ocean, where it can contribute to the pollution of coastal waters.

OR

Poaching is one of the main reasons behind the depletion of biodiversity-Prepare a list of any three such endangered wild animals resulting from it. Show the various methods of conservation of biodiversity with the help of a chart. [3+2=5]

Answer

Three endangered wild animals resulting from poaching:

1. Black rhinoceros: Poaching for their horns, which are used in traditional Chinese medicine, has led to a decline in black rhinoceros populations by over 97% in the past century.
2. African elephant: Poaching for ivory tusks has led to a decline in African elephant populations by over 60% in the past 50 years.
3. Bengal tiger: Poaching for their fur, bones, and other body parts has led to a decline in Bengal tiger populations by over 75% in the past 100 years.

Here is a chart showing the various methods of conservation of biodiversity:

Question 4.6

Three environmental problems of the Sunderbans are-

• imbalance in the numbers of prey and predators
• destruction of mangrove plants due to urbanisation
• rising sea level

Analyse the probable effects of the three problems. Mention the location and the name of one endangered species of a biodiversity hotspot distributed in and outside the geographical area of India. [3+2=5]

Answer

The probable effects of the three environmental problems of the Sundarbans:

• Imbalance in the numbers of prey and predators: This can lead to the extinction of prey species, as they will be hunted to extinction by predators. It can also lead to the overpopulation of predator species, which can then prey on other species in the ecosystem.
• Destruction of mangrove plants due to urbanisation: This can lead to the loss of habitat for many species that depend on mangroves for food and shelter. It can also lead to the erosion of coastlines, as mangroves help to protect them from the forces of the ocean.
• Rising sea level: This can inundate low-lying areas of the Sundarbans, displacing people and wildlife. It can also lead to the salinization of freshwater sources, making them unusable for drinking and irrigation.

One endangered species of a biodiversity hotspot distributed in and outside the geographical area of India is the Royal Bengal tiger. It is found in the Sundarbans, as well as in other parts of India, Bangladesh, and Nepal. The Royal Bengal tiger is listed as endangered on the IUCN Red List, and its population is declining due to habitat loss, poaching, and conflict with humans.

Here is a table summarizing the probable effects of the three environmental problems of the Sundarbans:

OR

Describe the nitrogen cycle with the help of a word diagram. Analyse any two problems which may arise if the nitrogen cycle is disturbed. [3+2=5]

Answer

1. Nitrogen fixation: Nitrogen gas is converted into ammonia by bacteria.
2. Ammonification: Ammonia is converted into nitrites and then nitrates by bacteria.
3. Nitrification: Nitrates are converted into nitrogen gas by bacteria.
4. Denitrification: Nitrates are converted back into nitrogen gas by bacteria.

Two problems that may arise if the nitrogen cycle is disturbed are:

• Decreased crop yields: Nitrogen is an essential nutrient for plants, so if the nitrogen cycle is disturbed, crop yields can decrease. This can lead to food shortages and malnutrition.
• Increased pollution: Nitrogen can contribute to smog and acid rain, which can have negative effects on human health and the environment.

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Group ‘E’
(For External Candidates Only)

5. Answer any four questions: [1×4=4]

Question 5.1

Write one feature of epithelial tissue.

Answer

One feature of epithelial tissue is that it is made up of tightly packed cells that form a sheet.

Question 5.2

What is the function of the ribosome?

Answer

The ribosome is a cell organelle that is responsible for protein synthesis.

Question 5.3

Write one function of parenchyma tissue.

Answer

Parenchyma tissue is a type of tissue that makes up the bulk of most organs.

Question 5.4

Write one advantage of self-pollination.

Answer

One advantage of self-pollination is that it is a more efficient way to reproduce than cross-pollination.

Question 5.5

Give an example of a proteolytic enzyme.

Answer

One example of a proteolytic enzyme is pepsin, which is found in the stomach. Pepsin helps to break down proteins in food so that they can be absorbed by the body.

6. Answer any three questions : [2×3=6]

Question 6.1

Write two differences between axon and dendron.

Answer

The two differences between axon and dendron in very short points:

• Axon:
  • Transmits electrical impulses away from the cell body.
  • Usually only one per neuron.
• Dendrite:
  • Receives electrical impulses from other neurons.
  • Many per neuron.

Question 6.2

Write the names of two nitrogenous excretory products of plants.

Answer

• Ammonia
• Urea

Question 6.3

Write one function for each of the mitochondria and centrosomes.

Answer

• Mitochondria: Mitochondria are the powerhouses of the cell, responsible for generating most of the cell’s energy.
• Centrosomes: Centrosomes are small organelles that help to organize the cell’s microtubules.

Question 6.4

Write the name of two sanctuaries of West Bengal.

Answer

The two sanctuaries of West Bengal

1. Sundarban National Park
2. Jaldapara National Park